A 38-year-old woman is evaluated during a routine examination. She is a mother of two children and works full time at a high-stress job. She smokes 10 cigarettes daily, eats fast food three times per week, and drinks two alcoholic beverages most nights. She does not exercise. Family history is noncontributory. She takes no medications.

On physical examination, the patient is afebrile, blood pressure is 122/76 mm Hg, and pulse rate is 80/min. BMI is 26. The remainder of the physical examination is normal.

Which of the following interventions will have the largest impact on this patient's health?